It is known that carbon dioxide may be sequestered by mineral carbonation. In nature, stable carbonate minerals and silica are formed by a reaction of carbon dioxide with natural silicate minerals:(Mg,Ca)xSiyOx+2y+xCO2x(Mg,Ca)CO3+ySiO2 
The reaction in nature, however, proceeds at very low reaction rates. The feasibility of such a reaction in process plants has been studied. These studies mainly aim at increasing the reaction rate.
The US department of energy has disclosed the reaction of finely ground serpentine (Mg3Si2O5(OH)4) or olivine (Mg2SiO4) in a solution of supercritical carbon dioxide and water to form magnesium carbonate. Under conditions of high temperature and pressure, 84% conversion of olivine has been achieved in 6 hours and a 80% conversion of pre-heated serpentine in less than an hour.
In WO02/085788, for example, is disclosed a process for mineral carbonation of carbon dioxide wherein particles of silicates selected from the group of ortho-, di-, ring, and chain silicates, are dispersed in an aqueous electrolyte solution and reacted with carbon dioxide.
It is known that orthosilicates or chain silicates can be relatively easy reacted with carbon dioxide to form carbonates and can thus suitably be used for carbon dioxide sequestration. Examples of magnesium or calcium orthosilicates suitable for mineral carbonation are olivine, in particular forsterite, and monticellite. Examples of suitable chain silicates are minerals of the pyroxene group, in particular enstatite or wollastonite. The more abundantly available magnesium or calcium silicate hydroxide minerals, for example serpentine and talc, are sheet silicates and are therefore more difficult to convert into carbonates. A very high activation energy is needed to convert these sheet silicate hydroxides into their corresponding ortho- or chain silicates.